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Calibration of the self-radar-cross-section of continuous-wave radars
No full textThis article presents a calibration method to eliminate measurement errors introduced by the own radar cross section (self-RCS) of continuous-wave (CW) radar systems, which focus on the measurement of relative target motions. By measuring the radar response of an unknown target located at known positions, the proposed procedure retrieves the calibration constants. They allow for eliminating the systematic errors associated with the multiple reflections between the radar device and the target, an effect initiated by the self-RCS. This improves the linearity of the overall transfer function, which enhances measurement accuracy and mitigates nonlinear distortion effects for vibration-sensing applications. The calibration approach is successfully validated by measurements in different conditions. In contrast to conventional techniques that implicitly neglect the self-RCS, the proposed technique achieves a superior and robust accuracy reaching one-thousandth of the operating wavelength
A comprehensive approach to incorporating intermolecular dispersion into the openCOSMO-RS model. Part 1. Halocarbons
No full textThe COSMO-RS (Conductor-like Screening Model for Real Solvents) is a predictive thermodynamic model that has found diverse applications in various domains like chemical engineering, environmental chemistry, nanotechnology, material science, and biotechnology. Its core concept involves calculating the screening charge density on the surface of each molecule and letting these surface patches interact with each other to calculate thermodynamic properties. In this study, we aim to enhance the performance of the open-source implementation openCOSMO-RS by incorporating dispersive interactions between the paired segments. Several parametrizations were systematically evaluated through the extensive regression analysis using a comprehensive database of Vapor-Liquid Equilibrium (VLE), Liquid-Liquid Equilibrium (LLE) and Infinite Dilution Activity Coefficients (IDACs). Furthermore, the influence of different combinatorial terms on the model performance was investigated. Our findings indicate that incorporating dispersive interactions significantly improves the accuracy of phase equilibrium predictions for halocarbons and refrigerant mixtures
Maximum Entropy-Mediated Liquid-to-Solid Nucleation and Transition
No full textMolecular dynamics (MD) simulations are a powerful tool for studying matter at the atomic scale. However, to simulate solids, an initial atomic structure is crucial for the successful execution of MD simulations but can be difficult to prepare due to insufficient atomistic information. At the same time, wide-angle X-ray scattering (WAXS) measurements can determine the radial distribution function (RDF) of atomic structures. However, the interpretation of RDFs is often challenging. Here, we present an algorithm that can bias MD simulations with RDFs by combining the information on the MD atomic interaction potential and the RDF under the principle of maximum relative entropy. We show that this algorithm can be used to adjust the RDF of one liquid model, e.g., the TIP3P water model, to reproduce the RDF and improve the angular distribution function (ADF) of another model, such as the TIP4P/2005 water model. In addition, we demonstrate that the algorithm can initiate crystallization in liquid systems, leading to both stable and metastable crystalline states defined by the RDF, e.g., crystallization of water to ice and liquid TiO2 to rutile or anatase. Finally, we discuss how this method can be useful for improving interaction models, studying crystallization processes, interpreting measured RDFs, or training machine-learned potentials
Investigation of hydrodynamic effects on controllable-pitch propellers during crash stop maneuvers
No full textModeling of temperature fields in milling of unidirectionally reinforced CFRP depending on the fibre orientation angle and the effective width of cut
No full textCFRP parts are conventionally used within various industries; however, during machining these components, the generated heat is a very relevant limiting factor. Exceeding the glass transition temperature can lead to workpiece degradation, reduced strength, and shorter lifetime. During up-cut milling of unidirectional (UD) CFRP with PCD cutters, the temperature was measured using thermocouples and a thermographic camera, while the cutting torque was measured with a rotating dynamometer. The maximum temperature increase at the machined surface, the heat flow from the machining zone into the material, and the ratio of heat flow to cutting power were simulated. An analytical model developed earlier for the temperature field in machining orthotropic composites with arbitrary fibre orientation was used. The results indicate that cutting power, heat flow, and the ratio of heat flow to cutting power exhibit approximate symmetry relative to the fibre orientation angle Φ = 90°. Introducing the concept of the fibre orientation symmetry angle is useful. Unexpected fractures of larger segments of remaining UD CFRP material occur at all feeds at higher fibre orientation and engagement angles within a small range of fibre cutting angles near 45°, significantly reducing the nominal width of cut and impairing results. The effective width of cut was evaluated based on the drop in cutting torque, measured at various fibre orientation angles, cutting speeds, feeds, and nominal widths of cut. The highest maximum temperature increase consistently occurs at Φ = 135°. As an overall effect, higher cutting speeds lead to increased cutting power, heat flow, and maximum temperature at the machined surface, but result in a smaller depth of the heat-affected zone. The simulations conclude that a higher fibre orientation symmetry angle leads to a higher equivalent heat flux, shorter thermal contact length, and reduced heat flow, and vice versa. In the future, the influence of different tools and composite materials needs to be investigated
Model-based autofocus for near-field phase retrieval
No full textThe phase problem is a well known ill-posed reconstruction problem of coherent lens-less microscopic imaging, where only the intensities of a complex wave-field are measured by the detector and the phase information is lost. For the reconstruction of sharp images from holograms in a near-field experimental setting, it is crucial to solve the autofocus problem, i.e., to precisely estimate the Fresnel number of the forward model. Otherwise, blurred out-of focus images that also can contain artifacts are the result. In general, a simple distance measurement at the experiment is not sufficiently accurate, thus the fine-tuning of the Fresnel number has to be done prior to the actual reconstructions. This can be done manually or automatically by an estimation algorithm. To automatize the process, as needed, e.g., for in-situ/operando experiments, different focus criteria have been widely studied in literature but are subjected to certain restrictions. The methods often rely on image analysis of the reconstructed image, making them sensitive to image noise and also neglecting algorithmic properties of the applied phase retrieval. In this paper, we propose a novel criterion, based on a model-matching approach, which improves autofocusing by also taking the underlying reconstruction algorithm, the forward model and the measured hologram into account. We derive a common autofocusing framework, based on a recent phase-retrieval approach and a downhill-simplex method for the automatic optimization of the Fresnel number. We further demonstrate the robustness of the framework on different data sets obtained at the nano imaging endstation of P05 at PETRA III (DESY, Hamburg) operated by Helmholtz-Zentrum Hereon
ULTRAS: Iterative Development of a Comprehensive Toolchain for Urban Air Mobility Simulation
No full textA modular urban air mobility (UAM) simulation toolchain was iteratively developed in the project ULTRAS (Urban Air Transportation Simulation). Twelve modules combined passenger demand, vertiports, routing, trajectories, sectorized capacities, costs, scheduling, and infrastructure scaling, communication, and control (GNC). Three iterations evolved modules from minimum viable products (MVP) to mature frameworks, adding and adapting assumptions, functionality, and interfaces. In each iteration, modules were integrated to a workflow, enabling comprehensive simulation and evaluation
Microplastics in sandy soils: alterations in thermal conductivity, surface albedo, and temperature
No full textRapid growth in plastic production has exacerbated disposal of plastic wastes in terrestrial ecosystems. Unfortunately, soils represent large reservoirs for disposal of microplastics (MPs). MPs infiltrate into the soil through various pathways and alter its intrinsic properties. Despite advances in understanding the impact of MPs on soil physical, biological, and hydrological processes, their influence on surface energy balance and soil temperature remains understudied. Such information is more necessary than ever, considering the ongoing changes to soil systems caused by climate variations and extremes. We conducted laboratory experiments on sandy soils to investigate how MPs with different characteristics impact soil temperature dynamics. The changes in the soil thermal conductivity and surface albedo, in the presence of polyethylene (PE) and polyvinylchloride (PVC) particles at various concentrations were measured. The results demonstrate that MPs, and particularly PVC, with amorphous characteristics may decrease effective thermal conductivity of sand by 38%. Moreover, the deposition of MPs at the surface of samples may increase surface albedo by 28% and 77% with addition of 5% PVC and 5% PE, respectively. Such effects are pronounced at higher soil moisture contents, facilitating migration and deposition of MPs on the surface. We ultimately examined the impact of changes in soil thermal and radiative properties on soil temperature dynamics by monitoring the thermal regime in drying sand columns. Our findings indicate that MPs significantly alter evaporative flux and subsurface temperature profile, hence providing insights into understanding the changes in soil energy balance due to the presence of MPs
Raster scan imaging in atomic force microscopy: new perspectives and potential of using signal and system theory
No full textRecent advances in high-performance Atomic Force Microscopy (AFM) allow real-time, atomic-scale imaging, but often require expensive equipment. This work revisits the AFM imaging technique and proposes a novel software-based solution for conventional AFMs operated in tapping mode to achieve both high-speed scans and high-resolution images using existing hardware. By treating an AFM scan as a signal modulation process, this method retrieves AFM images directly from signal demodulation. The method captures and analyzes the AFM probe's feedback signal, decomposing it into low- and high-frequency components. The low-frequency signal, representing raster scan motion, undergoes segmentation. The high-frequency signal, containing image information, is demodulated and segmented. These steps generate two sets of signals used to build the final AFM images. Validated on a standard AFM with extensive experiments at scanning speeds up to 240 μm/s, this flexible and easy-to-implementation method unlocks the potential for high-performance, affordable AFM in materials science research
Development of a Coextrusion Print Head for Non-Planar Load Oriented Additive Manufacturing of Carbon Fiber Reinforced Polymers
No full textIn order to realize the potential of high performance lightweight parts manufactured using the combination of fused filament fabrication (FFF) and carbon fiber reinforced polymers (CFRP), two main challenges have been identified for a print head design intended for load oriented non-planar printing. To address these objectives of enabling dynamic layer height variation and fiber cutting all while avoiding collisions in the printing system, this work presents the methodological development of a new specialized print head. By analyzing the process and taking the existing non-planar printing system into account, the relevant optimization parameters are identified and accurately defined. The methodological development is aligned with the VDI standard 2221 and includes a formal requirement analysis, parameter definition and functional structure. The solution space is discussed and partial solution are compared in detail, before the integration and final design are presented. The print head is physically realized, functionally verified by printing CFRP parts and shown to fulfill all set requirements. Minor necessary changes during manufacturing and construction of the system are discussed. Finally, the insight, definition, process analysis and final version are employed to present a further optimized design with a concrete methodological outlook on enabling the load oriented non-planar FFF of CFRP with this new highly optimized design